The role of iodide promoter in selective oxidation of methanol to formaldehyde

The interaction of a CH3I promoter and a commercial electrolytic silver catalyst was investigated using XPS, UPS and in situ confocal microprobe Raman spectroscopy. XPS and UPS results show evidence for formation of AgI on the surface of the silver catalyst. Interestingly, XPS results show no evidence for formation of any carbon species on the silver catalyst at room temperature, implying that CH3I can be used as a "pure" I-modifier in the catalytic oxidation of CH3OH to HCHO. UPS results show a positive work function change (delta phi> 0) for the I-modified catalysts. In situ Raman studies show that both the adsorption and reaction of methanol were promoted on the modified silver surface. The present experimental results provide not only an understanding of the surface chemistry of the silver catalyst but also a further understanding of the promotion effect of CH3I in the selective oxidation of CH3OH to HCHO.